User equipment

ABSTRACT

In one aspect of the present invention, user equipment includes a reception unit configured to receive first system information in a frequency block where a synchronization signal is placed and third system information in another frequency block; and a control unit configured to stop detecting the synchronization signal, (1) based on a parameter value determined from the first system information, (1-1) when a control channel search space for receiving second system information does not exist and (1-2) when the parameter value is within a predetermined range and (2) when the control channel search space for receiving the second system information does not exist based on a parameter value determined from the third system information.

TECHNICAL FIELD

The present invention relates to a field of radio communication, andmore specifically relates to user equipment.

BACKGROUND ART

In a Long Term Evolution (LTE) radio communication system and a LongTerm Evolution Advanced (LTE-A) radio communication system, userequipment (UE) performs cell search to find a cell to be connected forestablishing a physical channel. During cell search, the user equipmentobtains a physical cell identity (PCI) of the cell and performssynchronization with respect to radio frame timing.

In the LTE system, a primary synchronization signal (PSS) and asecondary synchronization signal (SSS) are defined as synchronizationsignals (SSs) for the purpose of efficient cell search. The PSS ismainly used for synchronization with respect to symbol timing anddetection of a local ID, and the SSS is used for synchronization withrespect to a radio frame and detection of a cell group ID. The PCI ofthe cell can be obtained by detecting the combination of the sequencesof these two signals.

Further, a physical broadcast channel (PBCH) includes basic systeminformation to be read by the user equipment immediately after cellsearch. The basic system information is referred to as a masterinformation block (MIB). A system information block (SIB) that is systeminformation other than the MIB is transmitted on a physical downlinkshared channel (PDSCH). In order to obtain the SIB, the user equipmentneeds to obtain control information transmitted on a physical downlinkcontrol channel (PDCCH).

PRIOR-ART DOCUMENTS Non-Patent Documents

-   [Non-Patent Document 1] 3GPP T538.211 V2.0.0 (2017-12)-   [Non-Patent Document 2] 3GPP T538.213 V2.0.0 (2017-12)

DISCLOSURE OF INVENTION Problem(s) to be Solved by the Invention

In the 3rd Generation Partnership Project (3GPP), a next generationcommunication standard (5G or NR) of LTE and LTE-A is under discussion.In NR, it is expected that user equipment will detect a synchronizationsignal and obtain a MIB that is part of system information upon initialaccess, as with LTE and LTE-A.

In LTE, a synchronization signal and a PBCH are placed at the center ofthe system band and a PDCCH is placed at a predetermined position in thesystem band. On the other hand, in NR, a synchronization signal and aPBCH is defined as a unit of a frequency block referred to as an SS/PBCHblock. One or more SS/PBCH blocks can be placed in a carrier frequencyband (see Non-Patent Document 1).

User equipment receives a synchronization signal in an SS/PBCH block,obtains a MIB, and then obtains remaining system information referred toas remaining minimum system information (RMSI) transmitted on a PDSCH.In order to obtain the RMSI, the user equipment needs to properlydetermine a search space (hereinafter referred to as a PDCCH searchspace) to find a PDCCH (see Non-Patent Document 2).

It is an object of the present invention to provide a solution for userequipment to properly determine a PDCCH search space.

Means for Solving the Problem(s)

In one aspect of the present invention, there is provision for userequipment, including:

a reception unit configured to receive first system information in afrequency block where a synchronization signal is placed and thirdsystem information in another frequency block; and

a control unit configured to stop detecting the synchronization signal,(1) based on a parameter value determined from the first systeminformation, (1-1) when a control channel search space for receivingsecond system information does not exist and (1-2) when the parametervalue is within a predetermined range and (2) when the control channelsearch space for receiving the second system information does not existbased on a parameter value determined from the third system information.

Advantageous Effect of the Invention

According to the present invention, user equipment can properlydetermine a PDCCH search space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a radiocommunication system according to an embodiment of the presentinvention.

FIG. 2 is a sequence diagram illustrating an operation of a radiocommunication system according to an embodiment of the presentinvention.

FIG. 3 is a flowchart illustrating an operation of user equipmentaccording to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between k_(SSB),RMSI-PDCCH-Config, and N_(GSCN) ^(Offset) in the case of FR1.

FIG. 5 is a diagram illustrating a relationship between k_(SSB),RMSI-PDCCH-Config, and N_(GSCN) ^(Offset) in the case of FR2.

FIG. 6 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 7 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 8 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 9 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 10 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 11 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 12 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 13 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 14 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 15 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 16 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 17 is an exemplary operation of user equipment according to anembodiment of the present invention.

FIG. 18 is a diagram illustrating an example of a functionalconfiguration of a base station according to an embodiment of thepresent invention.

FIG. 19 is a diagram illustrating an example of a functionalconfiguration of user equipment according to an embodiment of thepresent invention.

FIG. 20 is a diagram illustrating an example of a hardware configurationof a base station or user equipment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments will be described with reference to theaccompanying drawings. Note that the embodiments described below aremerely examples, and an embodiment to which the present invention can beapplied is not necessarily to be limited to the following embodiments.For example, in the embodiments, a radio communication system is assumedto be an NR system that is a succeeding system of an LTE system or anLTE-advanced system. However, the present invention is applicable toanother system in which user equipment determines a PDCCH search spaceto obtain system information.

<Overview of System Configuration and Operation>

FIG. 1 is a diagram illustrating a configuration of a radiocommunication system according to an embodiment of the presentinvention. As illustrated in FIG. 1, the radio communication systemaccording to this embodiment includes a base station (also referred toas a gNB) 100 and user equipment (also referred to as UE) 200. While onebase station 100 and one user equipment 200 are illustrated in FIG. 1 asan example, a plurality of base stations 100 or a plurality of userequipments 200 may be included.

The base station 100 can accommodate one or more (for example, three)cells (also referred to as “sectors”). When the base station 100accommodates a plurality of cells, the entire coverage area of the basestation 100 can be divided into a plurality of small areas, and in eachsmall area, a communication service can be provided through a basestation subsystem (for example, a small indoor base station remote radiohead (RRH)). The term “cell” or “sector” refers to a part or whole ofthe coverage area in which the base station and/or the base stationsubsystem provides a communication service. Further, the terms “basestation”, “gNB”, “eNB”, “cell”, and “sector” can be used interchangeablyin this specification. In some cases, the base station 100 is alsoreferred to as a fixed station, a NodeB, a gNodeB (gNB), an eNodeB(eNB), an access point, a femto cell, a small cell, or the like.

In some cases, the user equipment 200 is referred to as a mobilestation, a subscriber station, a mobile unit, a subscriber unit, awireless unit, a remote unit, a mobile device, a wireless device, awireless communication device, a remote device, a mobile subscriberstation, an access terminal, a mobile terminal, a wireless terminal, aremote terminal, a handset, a user agent, a mobile client, a client, orany other suitable term by those skilled in the art.

FIG. 2 is a sequence diagram illustrating an operation of a radiocommunication system according to an embodiment of the presentinvention. With reference to FIG. 2, initial access in the radiocommunication system illustrated in FIG. 1 is described. Initial accessis performed according to the following procedures: detection of asynchronization signal and obtainment of system information (MIB andRMSI). The system information may be referred to as broadcastinformation.

The user equipment 200 receives a PSS and an SSS transmitted from thebase station 100 in a predetermined frequency block (SS/PBCH block), anddetects a cell frequency, a reception timing, and a cell ID. Then, theuser equipment 200 obtains system information (MIB) transmitted on aPBCH in the SS/PBCH block where the PSS and the SSS is received (S101).One or more SS/PBCH blocks may be set in a carrier frequency band.

The user equipment 200 determines a PDCCH search space for receivingremaining system information (RMSI) based on the MIB transmitted on thePBCH (S103). The PDCCH search space is not a search space dedicated forthe user equipment 200, but a search space to be found in common by userequipments in the cell. Thus, the PDCCH search space is also referred toas a PDCCH common search space.

When the user equipment 200 receives, in the PDCCH search space, controlinformation necessary to receive RMSI, the user equipment 200 canreceive the RMSI transmitted on a PDSCH based on the control information(S105).

Even if the SS/PBCH block is determined, a PDCCH search space cannot bealways determined. For example, it is possible that the base station 100transmits a MIB in a certain SS/PBCH block, but does not transmit RMSIcorresponding to the MIB. In this case, the base station 100 may (1)instruct the user equipment 200 to detect another SS/PBCH block, or (2)specify a frequency range that is at least part of the carrier frequencyband and instruct the user equipment 200 to stop detecting an SS/PBCHblock in the frequency range in order to reduce a workload of the userequipment 200. The instructions regarding (1) and (2) can be implementedby changing a configuration value in the MIB transmitted from the basestation 100 to the user equipment 200.

In the latter case (2), it is possible that a malicious attackerinstalls a fake base station (fake gNB) to transmit SSs and a MIB in thecarrier frequency band of a certain operator and instructs userequipment to stop detecting an SS/PBCH block in the whole carrierfrequency band using the MIB. When the user equipment 200 receives theMIB transmitted from the fake base station, there is a risk that theuser equipment 200 cannot access a proper base station of the operator.In some cases, there is a risk that the user equipment 200 cannot accessa proper base station unless the user equipment 200 is restarted, orthere is a risk that the user equipment 200 cannot access a proper basestation even if the user equipment 200 moves around areas.

Even in the former case (1), when the user equipment 200 receives animproper MIB in the other SS/PBCH block, there is a risk that the userequipment 200 cannot access a proper base station.

For this reason, the following embodiment describes an example oflimiting a time period during which detection of an SS/PBCH block isstopped in a frequency band that is at least part of the carrierfrequency band. Specifically, detection of an SS/PBCH block is stoppedin the frequency band until a predetermined condition is satisfied.After the predetermined condition is satisfied, detection of an SS/PBCHblock in the frequency band is resumed. With this limitation, the userequipment 200 can access a proper base station after a certain timeperiod even if the user equipment 200 receives the MIB from the fakebase station.

Further, the following embodiment describes an example of stoppingdetecting an SS/BOCK block under a certain condition or limiting a timeperiod during which detection of an SS/PBCH block is stopped, even ifthe user equipment 200 receives the MIB in the other SS/PBCH block.

<Exemplary Operation in User Equipment>

FIG. 3 is a flowchart illustrating an operation of the user equipment200 according to an embodiment of the present invention.

The user equipment 200 detects an SS/PBCH block and obtains a MIB(S201). This step is the same as S101 in FIG. 2.

The user equipment 200 determines, based on the MIB, whether a PDCCHsearch space for receiving RMSI exists (S203). Whether a PDCCH searchspace exists may be determined based on a parameter value (k_(SSB))determined from the MIB. k_(SSB) is a parameter representing a frequencyoffset between an SS/PBCH and a PDCCH/PDSCH, and specifically isdetermined by a MIB parameter (ssb-subcarrierOffset) and a PBCH payload.k_(SSB) is also used for reception processing of the PDCCH. For example,when the carrier frequency band is FR1 (a frequency band lower than orequal to 6 GHz) and when k_(SSB)<=23 is satisfied, or when the carrierfrequency band is FR2 (a frequency band higher than 6 GHz) and whenk_(SSB)<=11 is satisfied, the user equipment 200 determines that a radioresource (control resource set) for the PDCCH search space exists.

When the base station 100 transmits a MIB in a certain SS/PBCH block andtransmits RMSI corresponding to the MIB, a PDCCH search space forreceiving RMSI exists and a radio resource for the PDCCH search spacealso exists. In this case (S203: Yes), the user equipment 200 finds thePDCCH search space to receive control information and receives RMSItransmitted on the PDSCH based on the control information (S205).

On the other hand, when the base station 100 transmits a MIB in acertain SS/PBCH block but does not transmit RMSI corresponding to theMIB, a PDCCH search space for receiving RMSI does not exist and a radioresource for the PDCCH search space does not exist, either. As describedabove, the base station 100 may (1) instruct the user equipment 200 todetect another SS/PBCH block, or (2) specify a frequency range that isat least part of the carrier frequency band and instruct the userequipment 200 to stop detecting an SS/PBCH block in the frequency rangein order to reduce a workload of the user equipment 200. For theinstructions regarding (1) and (2), the parameter value (k_(SSB))determined from the MIB can be used.

When a PDCCH search space does not exist (S203: No), the user equipment200 determines whether the parameter value (k_(SSB)) determined from theMIB is within a predetermined range (S207). For example, when thecarrier frequency band is FR1, the user equipment 200 determines whether24<=k_(SSB)<=30 is satisfied. For example, when the carrier frequencyband is FR2, the user equipment 200 determines whether 12<=k_(SSB)<=14is satisfied.

For example, when the carrier frequency band is FR1 and when24<=k_(SSB)<=30 is satisfied, or when the carrier frequency band is FR2and when 12<=k_(SSB)<=14 is satisfied, the user equipment 200 determinesthat another SS/PBCK block should be detected in order to determine aPDCCH search space and determines an SS/PBCH block to be detected(S209). The SS/PBCH block to be detected is determined based on k_(SSB)and RMSI-PDCCH-Config included in the MIB. RMSI-PDCCH-Config isconfiguration information necessary to receive RMSI on the PDCCH. Aglobal synchronization channel number GSCN of the SS/PBCH block to bedetected may be derived by N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset).N_(GSCN) ^(Reference) is a GSCN of the SS/PBCK block detected in stepS201 and N_(GSCN) ^(Offset) is a value determined from the tableillustrated in FIG. 4 or FIG. 5 according to a combination of k_(SSB)and RMSI-PDCCH-Config. FIG. 4 illustrates a relationship betweenk_(SSB), RMSI-PDCCH-Config, and N_(GSCN) ^(Offset) in the case of FR1,and FIG. 5 illustrates a relationship between k_(SSB),RMSI-PDCCH-Config, and N_(GSCN) ^(Offset) in the case of FR2. Therelationships illustrated in FIG. 4 and FIG. 5 may be determined inadvance in the specification.

After determining the SS/PBCH block to be detected, the operational flowreturns to step S201. The operational flow after returning to step S201is described below.

On the other hand, when the carrier frequency is FR1 and when k_(SSB)=31is satisfied (when 24<=k_(SSB)<=30 is not satisfied) or when the carrierfrequency is FR2 and when k_(SSB)=15 is satisfied (when 12<=k_(SSB)<=14is not satisfied), the user equipment 200 assumes that an SS/PBCH blockto be detected does not exist in a frequency range that is at least partof the carrier frequency band (S211). In this step, a predeterminedcondition is provided with respect to a time period during which theuser equipment 200 assumes that an SS/PBCH block to be detected does notexist. Accordingly, the user equipment 200 assumes that an SS/PBCH blockto be detected does not exist in a frequency range that is at least partof the carrier frequency band until the predetermined condition issatisfied. The frequency range in which an SS/PBCH block to be detecteddoes not exist may be derived by [N_(GSCN) ^(Reference)−N_(GSCN)^(Start), N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]N_(GSCN) ^(Start) andN_(GSCN) ^(End) may be determined based on RMSI-PDCCH-Config, forexample, based on a predetermined number of most significant bits and apredetermined number of least significant bits of RMSI-PDCCH-Config,respectively.

For example, the user equipment 200 assumes that an SS/PBCH block to bedetected does not exist in the frequency range [N_(GSCN)^(Reference)−N_(GSCN) ^(Start), N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]until detection of an SS/PBCH block is completed over frequencies otherthan the frequency range [N_(GSCN) ^(Reference)−N_(GSCN) ^(Start),N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]. It should be noted that thecondition that detection of an SS/PBCH block is completed may be acondition that detection of an SS/PBCH block is completed in the wholecarrier frequency band supported by the user equipment 200, or may be acondition that detection of an SS/PBCH block is completed in the carrierfrequency band in which detection of the SS/PBCH block is attempted instep S201. For example, when the user equipment 200 supports 700 MHzband, 1.5 GHz band, and 2 GHz band, the user equipment 200 may assumethat an SS/PBCH block to be detected does not exist in the frequencyband [N_(GSCN) ^(Reference)−N_(GSCN) ^(Start), N_(GSCN)^(Reference)+N_(GSCN) ^(End)] until detection of an SS/PBCH block iscompleted in all the frequency bands. Alternatively, when the userequipment 200 currently attempts to detect an SS/PBCH block in 1.5 GHzband, the user equipment 200 may assume that an SS/PBCH block to bedetected does not exist in the frequency band [N_(GSCN)^(Reference)−N_(GSCN) ^(Start), N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]until detection of an SS/PBCH block is completed in 1.5 GHz band.

For example, the user equipment 200 may alternatively assume that anSS/PBCH block to be detected does not exist in the frequency band[N_(GSCN) ^(Reference)−N_(GSCN) ^(Start), N_(GSCN) ^(Reference)+N_(GSCN)^(End)] until a predetermined time period (for example, 300 seconds) haselapsed. The predetermined time period (for example, 300 seconds) may befixed in the specification or may be provided to the user equipment 200as a parameter value in the MIB.

Then, the user equipment 200 determines whether an SS/PBCH block to bedetected over frequencies other than the frequency range [N_(GSCN)^(Reference)−N_(GSCN) ^(Start), N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]exists (S213). If it exists, the user equipment 200 determines anSS/PBCH block to be detected (S209), and then the operational flowreturns to step S201, where the user equipment 200 detects an SS/PBCHblock and obtains a MIB and RMSI as described above.

When an SS/PBCH block to be detected over frequencies other than thefrequency band [N_(GSCN) ^(Reference)−N_(GSCN) ^(Start), N_(GSCN)^(Reference)+N_(GSCN) ^(End)] does not exist, the operational flowreturns to step S211. At this moment, when the predetermined conditionis satisfied, for example, when detection of an SS/PBCH block overfrequencies other than the frequency range [N_(GSCN)^(Reference)−N_(GSCN) ^(Start), N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]is completed, or when the predetermined time period (for example, 300seconds) has elapsed, the SS/PBCH block in the frequency band [N_(GSCN)^(Reference)−N_(GSCN) ^(Start), N_(GSCN) ^(Reference)+N_(GSCN) ^(End)]is treated as an SS/PBCH block to be detected. The user equipment 200determines an SS/PBCH block to be detected (S209), and then theoperational flow returns to step S201, where the user equipment 200detects an SS/PBCH block and obtains a MIB and RMSI as described above.

With reference to FIGS. 6-17, the operational flow after determining anSS/PBCH block to be detected and after returning to step S201 is furtherdescribed. The operational flow as described below is independent ofS211 and S213 in FIG. 3, and S211 and S213 in FIG. 3 may not beperformed when the operational flow is executed.

As described above in step S201, the user equipment 200 obtains a newMIB (hereinafter referred to as MIB′) in the SS/PBCH block to bedetected.

As described above in step S203, the user equipment 200 determines,based on the MIB′, whether a PDCCH search space for receiving RMSIexists. Whether a PDCCH search space exists may be determined based on aparameter value (k_(SSB)) determined from the MIB′. For example, whenthe carrier frequency band is FR1 (a frequency band lower than or equalto 6 GHz) and when k_(SSB)<=23 is satisfied, or when the carrierfrequency band is FR2 (a frequency band higher than 6 GHz) and whenk_(SSB)<=11 is satisfied, the user equipment 200 determines that a radioresource (control resource set) for the PDCCH search space exists.

When the base station 100 transmits RMSI corresponding to the MIB′, aPDCCH search space for receiving RMSI exists and a radio resource forthe PDCCH search space also exists. In this case, the user equipment 200finds the PDCCH search space to receive control information and receivesRMSI transmitted on the PDSCH based on the control information.

On the other hand, when the base station 100 does not transmit RMSIcorresponding to the MIB′, a PDCCH search space for receiving RMSI doesnot exist and a radio resource for the PDCCH search space does notexist, either. Alternatively, when N_(GSCN) ^(Reference)+N_(GSCN)^(Offset) as determined above based on the MIB′ corresponds to the GSCNof the SS/PBCH block where the MIB has been detected in step S201, forexample, the user equipment 200 repeats reception of MIB and MIB′.

For this reason, when a PDCCH search space does not exist, the userequipment 200 assumes that an SS/PBCH block to be detected does notexist in a frequency range that is at least part of the carrierfrequency band and does not attempt to detect an SS/PBCH block in thefrequency range. In this case, a predetermined condition is providedwith respect to a time period during which the user equipment 200assumes that an SS/PBCH block to be detected does not exist.Accordingly, the user equipment 200 assumes that an SS/PBCH block to bedetected does not exist in a frequency range that is at least part ofthe carrier frequency band until the predetermined condition issatisfied. The frequency range in which an SS/PBCH block to be detecteddoes not exist may include both an SS/PBCH block corresponding toN_(GSCN) ^(Reference)+N_(GSCN) ^(End) determined based on the MIB′ andthe SS/PBCH block where the MIB has been initially received in step S201(see FIGS. 6-11, for example). More specifically, the user equipment 200does not attempt to decode a GSCN and a PCI of the SS/PBCH block wherethe MIB has been received and a GSCN and a PCI of the SS/PBCH blockwhere the MIB′ has been received.

FIG. 6 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist. FIG. 6 further illustrates thatthe user equipment 200 does not attempt to decode the SS/PBCH blockwhere the MIB has been received and the SS/PBCH block where the MIB′ hasbeen received until detection of an SS/PBCH block is completed in thewhole carrier frequency band supported by the user equipment 200.

FIG. 7 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist and N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on MIB′ indicates theSS/PBCH block where the MIB has been initially received (in other words,the user equipment 200 repeats reception of MIB and MIB′). FIG. 7further illustrates that the user equipment 200 does not attempt todecode the SS/PBCH block where the MIB has been received and the SS/PBCHblock where the MIB′ has been received until detection of an SS/PBCHblock is completed in the whole carrier frequency band supported by theuser equipment 200.

FIG. 8 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist. FIG. 8 further illustrates thatthe user equipment 200 does not attempt to decode the SS/PBCH blockwhere the MIB has been received and the SS/PBCH block where the MIB′ hasbeen received until detection of an SS/PBCH block is completed in thecarrier frequency band in which detection of the SS/PBCH block iscurrently attempted.

FIG. 9 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist and N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on MIB′ indicates theSS/PBCH block where the MIB has been initially received (in other words,the user equipment 200 repeats reception of MIB and MIB′). FIG. 9further illustrates that the user equipment 200 does not attempt todecode the SS/PBCH block where the MIB has been received and the SS/PBCHblock where the MIB′ has been received until detection of an SS/PBCHblock is completed in the carrier frequency band in which detection ofthe SS/PBCH block is currently attempted.

FIG. 10 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist. FIG. 10 further illustratesthat the user equipment 200 does not attempt to decode the SS/PBCH blockwhere the MIB has been received and the SS/PBCH block where the MIB′ hasbeen received until a predetermined time period (for example, 300seconds) has elapsed.

FIG. 11 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist and N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on MIB′ indicates theSS/PBCH block where the MIB has been initially received (in other words,the user equipment 200 repeats reception of MIB and MIB′). FIG. 11further illustrates that the user equipment 200 does not attempt todecode the SS/PBCH block where the MIB has been received and the SS/PBCHblock where the MIB′ has been received until a predetermined time period(for example, 300 seconds) has elapsed.

Alternatively, the frequency range in which an SS/PBCH block to bedetected does not exist may be a range between the SS/BPCH block wherethe MIB has been initially received in step S201 and the SS/PBCH blockwhere the MIB′ has been subsequently received in step S201 (see FIGS.12-17, for example). More specifically, the user equipment 200 does notattempt to decode an SS/PBCH block in a range between the GSCN of theSS/PBCH block where the MIB has been received and the GSCN of theSS/PBCH block where the MIB′ has been received.

FIG. 12 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist. FIG. 12 further illustratesthat the user equipment 200 does not attempt to decode an SS/PBCH blockin the range between the SS/PBCH block where the MIB has been receivedand the SS/PBCH block where the MIB′ has been received until detectionof an SS/PBCH block is completed in the whole carrier frequency bandsupported by the user equipment 200.

FIG. 13 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist and N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on MIB′ indicates theSS/PBCH block where the MIB has been initially received (in other words,the user equipment 200 repeats reception of MIB and MIB′). FIG. 13further illustrates that the user equipment 200 does not attempt todecode an SS/PBCH block in the range between the SS/PBCH block where theMIB has been received and the SS/PBCH block where the MIB′ has beenreceived until detection of an SS/PBCH block is completed in the wholecarrier frequency band supported by the user equipment 200.

FIG. 14 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist. FIG. 14 further illustratesthat the user equipment 200 does not attempt to decode an SS/PBCH blockin the range between the SS/PBCH block where the MIB has been receivedand the SS/PBCH block where the MIB′ has been received until detectionof an SS/PBCH block is completed in the carrier frequency band in whichdetection of the SS/PBCH block is currently attempted.

FIG. 15 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist and N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on MIB′ indicates theSS/PBCH block where the MIB has been initially received (in other words,the user equipment 200 repeats reception of MIB and MIB′). FIG. 15further illustrates that the user equipment 200 does not attempt todecode an SS/PBCH block in the range between the SS/PBCH block where theMIB has been received and the SS/PBCH block where the MIB′ has beenreceived until detection of an SS/PBCH block is completed in the carrierfrequency band in which detection of the SS/PBCH block is currentlyattempted.

FIG. 16 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist. FIG. 16 further illustratesthat the user equipment 200 does not attempt to decode an SS/PBCH blockin the range between the SS/PBCH block where the MIB has been receivedand the SS/PBCH block where the MIB′ has been received until apredetermined time period (for example, 300 seconds) has elapsed.

FIG. 17 illustrates that the user equipment 200 detects MIB′ in anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(Offset),but a PDCCH search space does not exist and N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on MIB′ indicates theSS/PBCH block where the MIB has been initially received (in other words,the user equipment 200 repeats reception of MIB and MIB′). FIG. 17further illustrates that the user equipment 200 does not attempt todecode an SS/PBCH block in the range between the SS/PBCH block where theMIB has been received and the SS/PBCH block where the MIB′ has beenreceived until a predetermined time period (for example, 300 seconds)has elapsed.

As described above, in each of the cases where the user equipment 200assumes that an SS/PBCH block to be detected does not exist, a conditionthat the user equipment 200 repeats reception of MIB and MIB′ may beconsidered in addition to a condition that a PDCCH search space does notexist (see FIGS. 7, 9, 11, 13, 15, and 17, for example). In other words,when a PDCCH search space does not exist and when N_(GSCN)^(Reference)+N_(GSCN) ^(Offset) determined based on the MIB′ correspondsto the SS/PBCH block where the MIB has been detected, the user equipment200 assumes that an SS/PBCH block to be detected does not exist in afrequency range that is at least part of the carrier frequency band anddoes not attempt to detect an SS/PBCH block in the frequency range. Inthis case, a predetermined condition is provided with respect to a timeperiod during which the user equipment 200 assumes that an SS/PBCH blockto be detected does not exist. Accordingly, the user equipment 200assumes that an SS/PBCH block to be detected does not exist in afrequency range that is at least part of the carrier frequency banduntil the predetermined condition is satisfied. The frequency range inwhich an SS/PBCH block to be detected does not exist may include both anSS/PBCH block corresponding to N_(GSCN) ^(Reference)+N_(GSCN) ^(End)determined based on the MIB′ and the SS/PBCH block where the MIB hasbeen initially received in step S201. Alternatively, the frequency rangein which an SS/PBCH block to be detected does not exist may be a rangebetween the SS/PBCH block where the MIB has been initially received instep S201 and the SS/PBCH block where the MIB′ has been subsequentlyreceived in step S201.

For example, the user equipment 200 assumes that an SS/PBCH block to bedetected does not exist in the frequency range as described above untildetection of an SS/PBCH block is completed over frequencies other thanthe frequency range. It should be noted that the condition thatdetection of an SS/PBCH block is completed may be a condition thatdetection of an SS/PBCH block is completed in the whole carrierfrequency band supported by the user equipment 200 (see FIGS. 6, 7, 12and 13, for example), or may be a condition that detection of an SS/PBCHblock is completed in the carrier frequency band in which detection ofthe SS/PBCH block is attempted in step S201 (see FIGS. 8, 9, 14, and 15,for example). For example, when the user equipment 200 supports 700 MHzband, 1.5 GHz band, and 2 GHz band, the user equipment 200 may assumethat an SS/PBCH block to be detected does not exist in the frequencyband until detection of an SS/PBCH block is completed in all thefrequency bands. Alternatively, when the user equipment 200 currentlyattempts to detect an SS/PBCH block in 1.5 GHz band, the user equipment200 may assume that an SS/PBCH block to be detected does not exist inthe frequency band until detection of an SS/PBCH block is completed in1.5 GHz band.

For example, the user equipment 200 may alternatively assume that anSS/PBCH block to be detected does not exist in the frequency band asdescribed above until a predetermined time period (for example, 300seconds) has elapsed (see FIGS. 10, 11, 16, and 17, for example). Thepredetermined time period (for example, 300 seconds) may be fixed in thespecification or may be provided to the user equipment 200 as aparameter value in the MIB (or MIB′).

The condition that the user equipment 200 does not attempt to decode anSS/PBCH block in any of FIGS. 6-17 (for example, until detection of anSS/PBCH block is completed in the whole carrier frequency band, untildetection of an SS/PBCH is completed in the carrier frequency band inwhich detection of the SS/PBCH is currently attempted, or until apredetermined time period has elapsed) is merely an example. When theuser equipment 200 receives an improper MIB according to which a PDCCHsearch space cannot be determined, the user equipment 200 may stopdetecting an SS/PBCH block.

Then, the user equipment 200 determines whether an SS/PBCH block to bedetected over frequencies other than the frequency range as describedabove exists. If it exists, the user equipment 200 determines an SS/PBCHblock to be detected, and then the operational flow returns to stepS201, where the user equipment 200 detects an SS/PBCH block and obtainsa MIB and RMSI as described above.

When an SS/PBCH block to be detected over frequencies other than thefrequency band as described above does not exist, the user equipment 200determines whether the predetermined condition is satisfied. Forexample, when detection of an SS/PBCH block over frequencies other thanthe frequency range is completed, or when the predetermined time period(for example, 300 seconds) has elapsed, the SS/PBCH block in thefrequency band is treated as an SS/PBCH block to be detected. The userequipment 200 determines an SS/PBCH block to be detected, and then theoperational flow returns to step S201, where the user equipment 200detects an SS/PBCH block and obtains a MIB and RMSI as described above.

In the description of FIGS. 3-17, although information such as k_(SSB),RMSI-PDCCH-Config, and so on transmitted on the PBCH is used as anexample for description, another kind of information transmitted on thePBCH or another channel may be alternatively used.

<Functional Configuration>

In the following, functional configurations of the base station 100 anduser equipment 200 that are capable of executing the processes describedabove are described.

FIG. 18 is a diagram illustrating an example of a functionalconfiguration of the base station 100 according to an embodiment of thepresent invention. As illustrated in FIG. 18, the base station 100includes a signal transmission unit 101, a signal reception unit 103, anSS/PBCH transmission processing unit 105, a PDCCH transmissionprocessing unit 107, a PDSCH transmission processing unit 109, and asystem information storage unit 111. FIG. 18 illustrates only mainfunctional units of the base station 100, and the functionalconfiguration illustrated in FIG. 18 is merely an example. Functionaldivision and names of the functions may be any functional division andnames are not limited to the example, provided that the operationaccording to the embodiment can be executed.

The signal transmission unit 101 includes a function to generate varioustypes of signals in the physical layer from signals in a higher layer tobe transmitted from the base station 100 and wirelessly transmit thegenerated signals. The signal reception unit 103 includes a function towirelessly receive various signals from the user equipment 200 andobtain signals in a higher layer from the received signals in thephysical layer.

It is assumed that each of the signal transmission unit 101 and thesignal reception unit 103 performs processing in a layer 1 (PHY), alayer 2 (MAC, RLC and PDCP), and a layer 3 (RRC). However, thefunctional configurations of the signal transmission unit 101 and thesignal reception unit 103 are not limited thereto.

The system information storage unit 111 stores system information to beprovided to the user equipment 200.

The SS/PBCH transmission processing unit 105 generates synchronizationsignals (PSS and SSS) and obtains system information (MIB) which isstored in the system information storage unit 111 and is to betransmitted on a PBCH. The SS/PBCH transmission processing unit 105causes the signal transmission unit 101 to transmit the synchronizationsignals and the MIB.

The PDCCH transmission processing unit 107 generates control informationwhich is necessary to receive a PDSCH and is to be transmitted on aPDCCH. The PDCCH transmission processing unit 107 causes the signaltransmission unit 101 to transmit the control information.

The PDSCH transmission processing unit 109 obtains system information(RMSI) which is stored in the system information storage unit 111 and isto be transmitted on the PDSCH. The PDSCH transmission processing unit109 causes the signal transmission unit 101 to transmit the RMSI.

FIG. 19 is a diagram illustrating an example of a functionalconfiguration of the user equipment 200 according to an embodiment ofthe present invention. As illustrated in FIG. 19, the user equipment 200includes a signal transmission unit 201, a signal reception unit 203, anSS/PBCH reception processing unit 205, a PDCCH reception processing unit207, a PDSCH reception processing unit 209, and a system informationstorage unit 211. FIG. 19 illustrates only main functional units of theuser equipment 200 particularly related to the embodiment of the presentinvention, and the functional configuration illustrated in FIG. 19 ismerely an example. Functional division and names of the functions may beany functional division and names are not limited to the example,provided that the operation according to the embodiment can be executed.

The signal transmission unit 201 includes a function to generate varioustypes of signals in the physical layer from signals in a higher layer tobe transmitted from the user equipment 200 and wirelessly transmit thegenerated signals. The signal reception unit 203 includes a function towirelessly receive various signals from the base station 100 and obtainsignals in a higher layer from the received signals in the physicallayer.

It is assumed that each of the signal transmission unit 201 and thesignal reception unit 203 performs processing in a layer 1 (PHY), alayer (MAC, RLC and PDCP), and a layer 3 (RRC). However, the functionalconfigurations of the signal transmission unit 201 and the signalreception unit 203 are not limited thereto.

The system information storage unit 211 stores system informationprovided by the base station 100.

The SS/PBCH reception processing unit 205 detects a cell frequency, areception timing, and a cell ID from synchronization signals (PSS andSSS) received by the signal reception unit 203. Further, the SS/PBCHreception processing unit 205 obtains system information (MIB)transmitted on the PBCH, as described in step S101 in FIG. 2, and storesthe MIB in the system information storage unit 211.

The PDCCH reception processing unit 207 determines a PDCCH search space,as described in step S103 in FIG. 2. The PDCCH reception processing unit207 finds the PDCCH search space and obtains control informationtransmitted on the PDCCH, as described in step S105 in FIG. 2.

The PDSCH reception processing unit 209 obtains system information(RMSI) transmitted on the PDSCH using the control information obtainedby the PDCCH reception processing unit 207, as described in step S105 inFIG. 2, and stores the RMSI in the system information storage unit 211.

<Hardware Configuration>

The block diagrams (FIG. 18 and FIG. 19) used to describe theabove-mentioned embodiment illustrate blocks of functional units. Thefunctional blocks (components) are implemented by an arbitrarycombination of hardware and/or software. A means for implementing eachfunctional block is not particularly limited. That is, each functionalblock may be implemented by one apparatus in which a plurality ofelements are physically and/or logically coupled or by a plurality ofapparatuses that are physically and/or logically separated from eachother and are connected directly and/or indirectly (for example, in awired manner and/or wirelessly).

For example, the base station 100 and the user equipment 200 accordingto the embodiment of the invention may function as a computer thatperforms the processes according to this embodiment. FIG. 14 is adiagram illustrating an example of a hardware configuration of the basestation 100 or the user equipment 200 according to this embodiment. Eachof the base station 100 and the user equipment 200 may be physicallyconfigured as a computer device including, for example, a processor1001, a memory 1002, a storage 1003, a communication device 1004, aninput device 1005, an output device 1006, and a bus 1007.

In the following description, the term “device” can be substituted with,for example, a circuit, an apparatus, or a unit. The hardwareconfiguration of the base station 100 or the user equipment 200 mayinclude one or a plurality of devices illustrated with 1001-1006 in FIG.8 or may not include some of the devices.

Each function of the base station 100 and the user equipment 200 may beimplemented by the following process: predetermined software (program)is read onto hardware such as the processor 1001 or the memory 1002, andthe processor 1001 performs an operation to control the communication ofthe communication device 1004, and/or the reading and/or writing of datafrom and/or to the memory 1002 and the storage 1003.

The processor 1001 operates, for example, an operating system to controlthe overall operation of the computer. The processor 1001 may be acentral processing unit (CPU) including, for example, an interface withperipheral devices, a control device, an arithmetic device, and aregister.

The processor 1001 reads a program (program code), a software module,and/or data from the storage 1003 and/or the communication device 1004to the memory 1002 and performs various types of processes according tothe program, the software module, or the data. A program that causes acomputer to perform at least some of the operations described in theembodiment may be used. For example, the SS/PBCH transmission processingunit 105, the PDCCH transmission processing unit 107, and the PDSCHtransmission processing unit 109 in the base station 100 may beimplemented by a control program that is stored in the memory 1002 andis executed by the processor 1001. Similarly, the SS/PBCH receptionprocessing unit 205, the PDCCH reception processing unit 207, and thePDSCH reception processing unit 209 in the user equipment 200 may beimplemented by a control program that is stored in the memory 1002 andis executed by the processor 1001. In the embodiment, theabove-mentioned various processes are performed by one processor 1001.However, the processes may be simultaneously or sequentially performedby two or more processors 1001. The processor 1001 may be mounted on oneor more chips. The program may be transmitted over the network through atelecommunication line.

The memory 1002 is a computer-readable recording medium and may include,for example, at least one of a read only memory (ROM), an erasableprogrammable ROM (EPROM), an electrically erasable programmable ROM(EEPROM), and a random access memory (RAM). The memory 1002 may be alsoreferred to as, for example, a register, a cache, or a main memory (mainstorage device). The memory 1002 can store, for example, an executableprogram (program code) and a software module that can perform theprocesses according to the embodiment of the invention.

The storage 1003 is a computer-readable recording medium and mayinclude, for example, at least one of an optical disk such as a compactdisc ROM (CD-ROM), a hard disk drive, a flexible disk, a magneto-opticaldisk (for example, a compact disc, a digital versatile disc, or aBlu-ray (registered trademark) disc), a smart card, a flash memory (forexample, a card, a stick, or a key drive), a floppy (registeredtrademark) disk, and a magnetic strip. The storage 1003 may be alsoreferred to as an auxiliary storage device. The above-mentioned storagemedium may be, for example, a database, a server, and other suitablemedia including the memory 1002 and/or the storage 1003.

The communication device 1004 is hardware (a transmission and receptiondevice) for communicating with a computer through a wired and/orwireless network and is also referred to as, for example, a networkdevice, a network controller, a network card, or a communication module.For example, the signal transmission unit 101 and the signal receptionunit 103 in the base station 100 may be implemented by the communicationdevice 1004. Similarly, the signal transmission unit 201 and the signalreception unit 203 in the user equipment 200 may be implemented by thecommunication device 1004.

The input device 1005 is an input unit (for example, a keyboard, amouse, a microphone, a switch, a button, or a sensor) that receives aninput from the outside. The output device 1006 is an output unit (forexample, a display, a speaker, or an LED lamp) that performs an outputprocess to the outside. The input device 1005 and the output device 1006may be integrated into a single device (for example, a touch panel).

Devices such as the processor 1001 and the memory 1002 are connected toeach other via the bus 1007 for information communication. The bus 1007may be a single bus or the devices may be connected to each other bydifferent buses.

Each of the base station 100 and the user equipment 200 may includehardware such as a microprocessor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a programmable logicdevice (PLD), and a field programmable gate array (FPGA). Some or all ofthe functional blocks may be implemented by the hardware. For example,the processor 1001 may be implemented by at least one of these hardwarecomponents.

Summary of Embodiments

As described above, in an embodiment of the present invention, there isprovision for user equipment including:

a reception unit configured to receive first system informationtransmitted from a base station in a frequency block where asynchronization signal is placed; and

a control unit configured to determine, based on a parameter valuedetermined from the first system information, whether a control channelsearch space for receiving second system information exists; when thecontrol channel search space does not exist, cause the reception unit toreceive third system information in another frequency block; determine,based on a parameter value determined from the third system information,whether the control channel search space for receiving the second systeminformation exists; and when the control channel search space does notexist, assume that a synchronization signal to be detected does notexist in a frequency range that is at least part of a carrier frequencyband until a predetermined condition is satisfied.

The control unit may stop detecting the synchronization signal in thefrequency range until the predetermined condition is satisfied, andresume detection of the synchronization signal after the predeterminedcondition is satisfied.

The user equipment can properly determine a PDCCH search space. Forexample, even if a malicious attacker installs a fake base station totransmit an improper MIB, a time period during which detection of anSS/PBCH block is stopped is limited, and thus it is possible to avoid asituation where the user equipment cannot access a proper base station.

The control unit may assume that the synchronization signal to bedetected does not exist in the frequency range until detection of asynchronization signal over frequencies other than the frequency rangeis completed.

The control unit may assume that the synchronization signal to bedetected does not exist in the frequency range until a predeterminedtime period has elapsed.

Since the user equipment need only manage the time period using a timer,detection of a synchronization signal can be resumed with a simplifiedoperation.

Supplementary Explanation of Embodiments

Each aspect/embodiment described in the specification may be applied tosystems using Long Term Evolution (LTE), LTE-Advanced (LTE-A), SUPER 3G,IMT-Advanced, 4G, 5G, Future Radio Access (FRA), W-CDMA (registeredtrademark), GSM (registered trademark), CDMA2000, Ultra Mobile Broadband(UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20,Ultra-WideBand (UWB), Bluetooth (registered trademark), and othersuitable systems and/or next-generation systems that have functionalityenhanced based on these systems.

The terms “system” and “network” used in the specification areinterchangeably used.

In the specification, a specific operation performed by the base stationmay be performed by an upper node of the base station. In a networkhaving one or a plurality of network nodes including the base station,it is clearly understood that various operations performed forcommunication with the user equipment can be performed by the basestation and/or a network node (for example, including an MME or an S-GWwithout limitation) other than the base station. The number of networknodes other than the base station is not limited to one, and a pluralityof other network nodes (for example, an MME and an S-GW) may be combinedwith each other.

Information or the like can be output from a higher layer (or a lowerlayer) to a lower layer (or a higher layer). Information or the like maybe input or output via a plurality of network nodes.

The input or output information or the like may be stored in a specificlocation (for example, a memory) or may be managed in a managementtable. The input or output information or the like may be overwritten,updated, or edited. The output information or the like may be deleted.The input information or the like may be transmitted to anotherapparatus.

The transmission of information is not limited to theaspects/embodiments described in the specification and may be performedby other means. For example, the transmission of information may beperformed by physical layer signaling (for example, downlink controlinformation (DCI) or uplink control information (UCI)), higher layersignaling (for example, radio resource control (RRC) signaling, mediumaccess control (MAC) signaling, or broadcast information (a masterinformation block (MIB) and a system information block (SIB))), anothersignal, or a combination thereof. The RRC signaling may be also referredto as an RRC message and may be, for example, an RRC connection setupmessage or an RRC connection reconfiguration message.

Determination may be made based on a value (0 or 1) represented by 1bit, may be made based on a true or false value (boolean: true orfalse), or may be made based on comparison with a numerical value (forexample, comparison with a predetermined value).

Regardless of the fact that software is referred to as software,firmware, middleware, a microcode, a hardware description language, oranother name, the software is broadly interpreted to include aninstruction, an instruction set, a code, a code segment, a program code,a program, a sub-program, a software module, an application, a softwareapplication, a software package, a routine, a subroutine, an object, anexecutable file, an execution thread, a procedure, a function, or thelike.

Software, an instruction, or the like may be transmitted or received viaa transmission medium. For example, when software is transmitted from awebsite, a server, or another remote source using a wired technologysuch as a coaxial cable, an optical cable, a twisted pair, and a digitalsubscriber line (DSL) and/or a wireless technology such as an infraredray, radio, and microwaves, the wired technology and/or the wirelesstechnology is included in the definition of a transmission medium.

The information, the signal, and the like described in the specificationmay be represented using any of various technologies. For example, thedata, the instruction, the command, the information, the signal, thebit, the symbol, the chip, and the like mentioned throughout thedescription may be represented by a voltage, a current, anelectromagnetic wave, a magnetic field, or a magnetic particle, anoptical field or a photon, or any combination thereof.

The terms described in the specification and/or terms necessary tounderstand the specification may be replaced with terms that have sameor similar meanings. For example, a channel and/or a symbol may be asignal. A signal may be a message. A component carrier (CC) may bereferred to as a carrier frequency, a cell, or the like.

The information, the parameter, or the like described in thespecification may be represented by an absolute value, may berepresented by a relative value from a predetermined value, or may berepresented by another piece of corresponding information. For example,a radio resource may be indicated using an index.

The names used for the above-described parameters are not limited in anyrespect. Further, a numerical expression or the like in which theparameters are used can be different from the numerical expressiondisclosed explicitly in the specification. Since various channels (forexample, a PUCCH and a PDCCH) and information elements (for example,TPC) can be identified with any suitable names, various names allocatedto the various channels and the information elements are not limited inany respect.

The terms “determining” and “deciding” used in the specification includevarious operations. The terms “determining” and “deciding” can include,for example, “determination” and “decision” for calculating, computing,processing, deriving, investigating, looking-up (for example, looking-upin a table, a database, or another data structure), and ascertainingoperations. In addition, the terms “determining” and “deciding” caninclude “determination” and “decision” for receiving (for example,information reception), transmitting (for example, informationtransmission), input, output, and accessing (for example, accessing datain a memory) operations. The terms “determining” and “deciding” caninclude “determination” and “decision” for resolving, selecting,choosing, establishing, and comparing operations. That is, the terms“determining” and “deciding” can include “determination” and “decision”for any operation.

The term “based on” used in the specification does not mean “only basedon” unless otherwise stated. In other words, the term “based on” meansboth “only based on” and “at least based on”.

When reference is made to elements in which terms “first,” “second,” andthe like are used in the specification, the number or the order of theelements is not generally limited. These terms can be used in thespecification as a method to conveniently distinguish two or moreelements from each other. Accordingly, reference to first and secondelements does not imply that only two elements are employed or the firstelement is prior to the second element in some ways.

The terms “include” and “including” and the modifications thereof areintended to be inclusive, similarly to the term “comprising”, as long asthey are used in the specification or the claims. In addition, the term“or” used in the specification or the claims does not mean exclusive OR.

In each aspect/embodiment described in the specification, for example,the order of the processes in the procedure, the sequence, and theflowchart may be changed unless a contradiction arises. For example, forthe method described in the specification, elements of various steps arepresented in the exemplified order. However, the invention is notlimited to the presented specific order.

The aspects/embodiments described in the specification may beindividually used, may be combined, or may be switched during execution.In addition, transmission of predetermined information (for example,transmission of “being X”) is not limited to being performed explicitly,but may be performed implicitly (for example, the transmission of thepredetermined information is not performed).

The invention has been described in detail above. It will be apparent tothose skilled in the art that the invention is not limited to theembodiments described in the specification. Various modifications andchanges can be made, without departing from the scope and spirit of theinvention described in the claims. Therefore, the embodiments describedin the specification are illustrative and do not limit the invention.

The present international application is based on and claims the benefitof priority of Japanese Patent Application No. 2018-079103 filed on Apr.17, 2018, the entire contents of which are hereby incorporated byreference.

DESCRIPTION OF NOTATIONS

-   -   100 base station    -   101 signal transmission unit    -   103 signal reception unit    -   105 SS/PBCH transmission processing unit    -   107 PDCCH transmission processing unit    -   109 PDSCH transmission processing unit    -   111 system information storage unit    -   200 user equipment    -   201 signal transmission unit    -   203 signal reception unit    -   205 SS/PBCH reception processing unit    -   207 PDCCH reception processing unit    -   209 PDSCH reception processing unit    -   211 system information storage unit

1. A terminal, comprising: a reception unit configured to receive firstsystem information in a frequency block where a synchronization signalis placed and third system information in another frequency block; and acontrol unit configured to stop detecting the synchronization signal,(1) based on a parameter value determined from the first systeminformation, (1-1) when a control channel search space for receivingsecond system information does not exist and (1-2) when the parametervalue is within a certain range and (2) when the control channel searchspace for receiving the second system information does not exist basedon a parameter value determined from the third system information. 2.The terminal as claimed in claim 1, wherein the control unit assumesthat a synchronization signal to be detected does not exist untildetection of a synchronization signal in a frequency range that is atleast part of a carrier frequency band is completed.
 3. The terminal asclaimed in claim 1, wherein the control unit assumes that asynchronization signal to be detected does not exist in a frequencyrange that is at least part of a carrier frequency band until a certaincondition is satisfied, (1) based on the parameter value determined fromthe first system information, (1-1) when the control channel searchspace for receiving the second system information does not exist and(1-3) when the parameter value is not within the certain range.
 4. Theterminal as claimed in claim 3, wherein the control unit assumes thatthe synchronization signal to be detected does not exist in thefrequency range until a certain time period has elapsed.
 5. The terminalas claimed in claim 3, wherein the control unit resumes detection of thesynchronization signal in the frequency range after the certaincondition is satisfied.
 6. The terminal as claimed in claim 1, whereinthe first system information is MIB, the second system information issystem information transmitted on a shared channel, and the controlchannel search space is a PDCCH search space to be detected in common byterminals in a cell.
 7. A synchronization signal detection method in aterminal, comprising the steps of: receiving first system information ina frequency block where a synchronization signal is placed and thirdsystem information in another frequency block; and stopping detectingthe synchronization signal, (1) based on a parameter value determinedfrom the first system information, (1-1) when a control channel searchspace for receiving second system information does not exist and (1-2)when the parameter value is within a certain range and (2) when thecontrol channel search space for receiving the second system informationdoes not exist based on a parameter value determined from the thirdsystem information.
 8. The terminal as claimed in claim 2, wherein thecontrol unit assumes that a synchronization signal to be detected doesnot exist in a frequency range that is at least part of a carrierfrequency band until a certain condition is satisfied, (1) based on theparameter value determined from the first system information, (1-1) whenthe control channel search space for receiving the second systeminformation does not exist and (1-3) when the parameter value is notwithin the certain range.
 9. The terminal as claimed in claim 4, whereinthe control unit resumes detection of the synchronization signal in thefrequency range after the certain condition is satisfied.
 10. Theterminal as claimed in claim 2, wherein the first system information isMIB, the second system information is system information transmitted ona shared channel, and the control channel search space is a PDCCH searchspace to be detected in common by terminals in a cell.
 11. The terminalas claimed in claim 3, wherein the first system information is MIB, thesecond system information is system information transmitted on a sharedchannel, and the control channel search space is a PDCCH search space tobe detected in common by terminals in a cell.
 12. The terminal asclaimed in claim 4, wherein the first system information is MIB, thesecond system information is system information transmitted on a sharedchannel, and the control channel search space is a PDCCH search space tobe detected in common by terminals in a cell.
 13. The terminal asclaimed in claim 5, wherein the first system information is MIB, thesecond system information is system information transmitted on a sharedchannel, and the control channel search space is a PDCCH search space tobe detected in common by terminals in a cell.